This invention relates generally to the field of telephony, and more particularly to an improved frame construction used in a telephone office for interconnecting individual subscriber pairs to office switching systems.
Over the last decade, old style mechanical switching systems have been replaced with solid state digital switching systems, which offer many advantages, and, of course, substantially all new installations are made on a digital switching system basis. With such installation, there has arisen a need to enable the testing and checking of such systems for proper function, which was not necessary in the case of mechanical switching systems where malfunctions could be manually observed by service personnel without making conductivity tests. While testing of an individual subscriber circuit can be done by placing test currents on the subscriber line using switching equipment, or by resort to test fields on connector blocks or available at the ends of protector modules, the testing of the circuits themselves has not been as readily available. Thus, when a malfunction occurs, which cannot be traced to a subscriber line, and which is believed to lie in the plant equipment area, access to such switching equipment for test purposes has not been easy, and the ability to connect other switching equipment in line pending repair has not been facilitated.
As a result of such difficulty, there has been developed, a variety of connector blocks including jackfields which may be interconnected using patch cords, whereby circuitry may be rerouted between inside plant and outside cables with a minimum of difficulty. These structures are useful not only for effecting digital switch cutover, but also permit, for example, the rerouting of traffic interrupted by a cut cable which can be reconnected through a third office by simple cross connections.
While such jackfield elements can be installed on almost any known main frame construction, as usual, the principal problem is that of maximum space utilization. Unfortunately, because of the large number of jack outlets, and their relatively larger size as contrasted with a wire wrap pin, the effective circuit density per unit area nowhere approaches the high density possible with modern circuit block construction. If, therefore, it is desired to have a group of subscriber circuits interfaced with particular office equipment, and have all of the interconnections on a single main frame, it is apparent that conventional architecture relative to the location of the interconnecting elements be modified. Most main frames, assuming usual building limitations, are about twelve feet high, as a result of which the upper areas are not readily accessible to service personnel without the assistance of a short ladder or a similar device. On the other hand, in the case of a frame, the function of which is to provide manually made cross connections, using state-of-the art jackfield blocks, the jackfields need occupy less than forty percent of the total available area on the frame, preferably at one location, and readily accessible to service personnel without the need of resorting to a ladder or similar device.